WSJT-X on Ubuntu

FT8 has taken the HF DX world by storm, working for < -24 dB SNR signals with 15 second transmission time per message. The PC clock should have time error < 2 seconds for proper decode, which is handled automatically on Linux via NTP.

The WSJT-X program is very robust and reliable. It decodes multiple signals at once, and is very good even for overlapping signals via signal subtraction, particularly for FT8.

Install WSJT-X on Linux

  1. Download WSJT-X, which includes WSPR, FT8 and JT65/JT9 among others. Most Linux computers use the wsjtx*amd64.deb version. The Raspberry Pi uses the wsjtx*armhf.deb version.
  2. Install WSJT-X
    gdebi wsjtx*.deb
    

JT9/JT65 divider frequency

I set 2600 Hz as the divider between JT65 (below 2600 Hz) and JT9 (above 2600 Hz). Some people use +/- 100 Hz from this.

Transmit power

Control your output power with your sound card output level, NOT with your radio’s RF power control. If you have your radio transmitter slamming hard into ALC (by maxing audio output and turning RF power control down) you will be splattering (interfering with adjacent frequencies), just like other digital modes in general. Most people use 1 to 25 Watts transmit power for JT65 and JT9.

60 meters

For 60 meters, remember that 2.8 kHz is the upper edge of the channel for USA users.

Tips for older radios

Older radios often have too-narrow filters. These filters do not have infinitely steep skirts, but you will certainly take an SNR penalty outside the passband. I notice that most stations operate at no less than 300-400 Hz above carrier frequency, so by using your IF shift (or PBT), you can cover from 400-2800 Hz, with ability to hear stronger 3000 Hz JT9 stations. It’s a tradeoff between missing stations on the edge of either band. I notice that JT65 DX sometimes does down as low as 300 Hz (typically accomplished by their radio using Split TX frequency). I have also see JT9 as high as 3500 Hz and beyond.

SDR is best

If you are interested in contributing to ionospheric science, you need a radio that receives on multiple bands, multiple modes simultaneously. That is capturing CW, JT65, JT9, WSPR, etc. simultaneously. You can do single-band, multimode reception with a FlexRadio 1500, RFSpace SDR-IQ, et al. Simultaneous multi-band reception can be accomplished with a bank of SoftRock receivers or a QS1R, and so on. Another cost-effective and powerful way is to do it yourself with an instrument like Red Pitaya, but you might start with a commercial SDR receiver and go from there.

Notes

If you get “a later version is already installed” error on upgrading WSJT-X, remove the existing version with

dpkg -r wsjtx

and then install the new WSJT-X version. Your configuration settings will be preserved.

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